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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Alternate methods of applying diffusants to silicon solar cells

Low-melting phosphate and borate glasses were screen printed on silicon wafers and heated to form n and p junctions. Data on surface appearance, sheet resistance and junction depth are presented. Similar data are reported for vapor phase transport from sintered aluminum metaphosphate and boron-containing glass-ceramic solid sources. Simultaneous diffusion of an N(+) layer with screen-printed glass and a p(+) layer with screen-printed Al alloy paste was attempted. No p(+) back surface field formation was achieved. Some good cells were produced but the heating in an endless-belt furnace caused a large scatter in sheet resistance and junction depth for three separate lots of wafers.

Brock, T. W.↗
NASA NTRS2000

Remobilizing the Interfaces of Thermocapillary Driven Bubbles Retarded by the Adsorption of a Surfactant Impurity on the Bubble Surface

Thermocapillary migration is a method for moving bubbles in space in the absence of buoyancy. A temperature gradient is applied to the continuous phase in which a bubble is situated, and the applied gradient impressed on the bubble surface causes one pole of the drop to be cooler than the opposite pole. As the surface tension is a decreasing function of temperature, the cooler pole pulls at the warmer pole, creating a flow which propels the bubble in the direction of the warmer fluid. A major impediment to the practical use of thermocapillarity to direct the movement of bubbles in space is the fact that surfactant impurities which are unavoidably present in the continuous phase can significantly reduce the migration velocity. A surfactant impurity adsorbed onto the bubble interface is swept to the trailing end of the bubble. When bulk concentrations are low (which is the case with an impurity), diffusion of surfactant to the front end is slow relative to convection, and surfactant collects at the back end of the bubble. Collection at the back lowers the surface tension relative to the front end setting up a reverse tension gradient. For buoyancy driven bubble motions in the absence of a thermocapillarity, the tension gradient opposes the surface flow, and reduces the surface and terminal velocities (the interface becomes more solid-like). When thermocapillary forces are present, the reverse tension gradient set up by the surfactant accumulation reduces the temperature tension gradient, and decreases to near zero the thermocapillary velocity. The objective of our research is to develop a method for enhancing the thermocapillary migration of bubbles which have been retarded by the adsorption onto the bubble surface of a surfactant impurity, Our remobilization theory proposes to use surfactant molecules which kinetically rapidly exchange between the bulk and the surface and are at high bulk concentrations. Because the remobilizing surfactant is present at much higher concentrations than the impurity, it adsorbs to the bubble much faster than the impurity when the bubble is formed, and thereby prevents the impurity from adsorbing onto the surface. In addition the rapid kinetic exchange and high bulk concentration maintain a saturated surface with a uniform surface concentrations. This prevents retarding surface tension gradients and keeps the velocity high. In our first report last year, we detailed experimental results which verified the theory of remobilization in ground based experiments in which the steady velocity of rising bubbles was measured in a continuous phase consisting of a glycerol/water mixture containing a polyethylene glycol surfactant C12E6 (CH3(CH2)11(OCH2CH2)6OH). In our report this year, we detail our efforts to describe theoretically the remobilization observed. We construct a model in which a bubble rises steadily by buoyancy in a continuous (Newtonian) viscous fluid containing surfactant with a uniform far field bulk concentration. We account for the effects of inertia as well as viscosity in the flow in the continuous phase caused by the bubble motion (order one Reynolds number), and we assume that the bubble shape remains spherical (viscous and inertial forces are smaller than capillary forces, i e. small Weber and capillary numbers). The surfactant distribution is calculated by solving the mass transfer equations including convection and diffusion in the bulk, and finite kinetic exchange the bulk and the surface. Convective effects dominate diffusive mass transfer in the bulk of the liquid (high Peclet numbers) except in a thin boundary layer near the surface. A finite volume method is used to numerically solve the hydrodynamic and mass transfer equations on a staggered grid which accounts specifically for the thin boundary layer. We present the results of the nondimensional drag as a function of the bulk concentration of surfactant for different rates of kinetic exchange, from which we develop criteria for the concentration necessary to develop a prescribed degree of remobilization. The criteria compare favorably with the experimental results.

Palaparthi, Ravi↗
NASA NTRS1983

Measurements of the scattering of sound by a line vortex

This paper presents measurements of the phase and magnitude of the scattered field arising from the incidence of a monochromatic plane sound field as a steady vortex. The amplitude of the scattered field was found to vary linearly with the vortex strength, and with the incident wave amplitude and frequency as predicted by solutions based on the Born approximation. The scattered field was observed to be nonsingular in the incidence direction, and this was similar to predictions by the Parabolic Equation Method (PEM) rather than the Born approximation, which predicts singular behavior in the incidence direction.

Horne, W. C.↗
NASA NTRS2002

Gas-Phase Reaction Pathways and Rate Coefficients for the Dichlorosilane-Hydrogen and Trichlorosilane-Hydrogen Systems

As part of NASA Ames Research Center's Integrated Process Team on Device/Process Modeling and Nanotechnology our goal is to create/contribute to a gas-phase chemical database for use in modeling microelectronics devices. In particular, we use ab initio methods to determine chemical reaction pathways and to evaluate reaction rate coefficients. Our initial studies concern reactions involved in the dichlorosilane-hydrogen (SiCl2H2--H2) and trichlorosilane-hydrogen (SiCl2H-H2) systems. Reactant, saddle point (transition state), and product geometries and their vibrational harmonic frequencies are determined using the complete-active-space self-consistent-field (CASSCF) electronic structure method with the correlation consistent polarized valence double-zeta basis set (cc-pVDZ). Reaction pathways are constructed by following the imaginary frequency mode of the saddle point to both the reactant and product. Accurate energetics are determined using the singles and doubles coupled-cluster method that includes a perturbational estimate of the effects of connected triple excitations (CCSD(T)) extrapolated to the complete basis set limit. Using the data from the electronic structure calculations, reaction rate coefficients are obtained using conventional and variational transition state and RRKM theories.

Dateo, Christopher E.↗
NASA NTRS2002

Characterization of iron, manganese, and copper synthetic hydroxyapatites by electron paramagnetic resonance spectroscopy

The incorporation of micronutrients (e.g., Fe, Mn, Cu) into synthetic hydroxyapatite (SHA) is proposed for slow release of these nutrients to crops in NASA's Advanced Life Support (ALS) program for long-duration space missions. Separate Fe3+ (Fe-SHA), Mn2+ (Mn-SHA), and Cu2+ (Cu-SHA) containing SHA materials were synthesized by a precipitation method. Electron paramagnetic resonance (EPR) spectroscopy was used to determine the location of Fe3+, Mn2+, and Cu2+ ions in the SHA structure and to identify other Fe(3+)-, Mn(2+)-, and Cu(2+)-containing phases that formed during precipitation. The EPR parameters for Fe3+ (g=4.20 and 8.93) and for Mn2+ (g=2.01, A=9.4 mT, D=39.0 mT and E=10.5 mT) indicated that Fe3+ and Mn2+ possessed rhombic ion crystal fields within the SHA structure. The Cu2+ EPR parameters (g(z)=2.488, A(z)=5.2 mT) indicated that Cu2+ was coordinated to more than six oxygens. The rhombic environments of Fe3+ and Mn2+ along with the unique Cu2+ environment suggested that these metals substituted for the 7 or 9 coordinate Ca2+ in SHA. The EPR analyses also detected poorly crystalline metal oxyhydroxides or metal-phosphates associated with SHA. The Fe-, Mn-, and Cu-SHA materials are potential slow release sources of Fe, Mn, and Cu for ALS and terrestrial cropping systems.

NASA Center JSC↗
NASA NTRS1984

The Dynamics of Ionospheric D Region over East Siberia

Some main results of experimental investigations of the dynamical regime of the ionospheric D-region over East Siberia are presented. Regular measurements of horizontal ionospheric drifts by the radio method of closely spaced receivers, using a long wavelength transmitter operating at a frequency of 200 kHz, were carried out near Irkutsk, USSR, since 1975. The seasonal and inter-annual variations of prevailing wind (zonal and meridional), and amplitudes and phases of semi-diurnal tides are investigated. Evidence is presented to show the response of D-region dynamics to stratospheric warmings. Planetary and gravity waves are found in the wind field. Comparison with results of analogous measurements in Central Europe (Collm, GDR) reveals a longitudinal effect on the dynamical regime of the mid-latitude lower thermosphere.

Kazimirovsky, E. S.↗
NASA NTRS2009

Ultra High Temperature Ceramics' Processing Routes and Microstructures Compared

Ultra High Temperature Ceramics (UHTCs), such as HfB2 and ZrB2 composites containing SiC, are known to have good thermal shock resistance and high thermal conductivity at elevated temperatures. These UHTCs have been proposed for a number of structural applications in hypersonic vehicles, nozzles, and sharp leading edges. NASA Ames is working on controlling UHTC properties (especially, mechanical properties, thermal conductivity, and oxidation resistance) through processing, composition, and microstructure. In addition to using traditional methods of combining additives to boride powders, we are preparing UHTCs using coat ing powders to produce both borides and additives. These coatings and additions to the powders are used to manipulate and control grain-boundary composition and second- and third-phase variations within the UHTCs. Controlling the composition of high temperature oxidation by-products is also an important consideration. The powders are consolidated by hot-pressing or field-assisted sintering (FAS). Comparisons of microstructures and hardness data will be presented.

Gusman, Michael↗
NASA NTRS2006

A Magnetic Field Response Recorder: A New Tool for Measurement Acquisition

A magnetic field response recorder was developed to facilitate a measurement acquisition method that uses magnetic fields to power and to interrogate all sensors. Sensors are designed as electrically passive inductive-capacitive or passive inductive-capacitive-resistive circuits that produce magnetic field responses when electrically activated by oscillating magnetic fields. When electrically activated, the sensor's magnetic field response attributes (frequency, amplitude and bandwidth) correspond to the one or more physical states that each sensor measures. The response recorder makes it possible to simultaneously measure two unrelated physical properties using this class of sensors. The recorder is programmable allowing it to analyze one or more response attributes simultaneously. A single sensor design will be used to demonstrate that the acquisition method and the sensor example can be used to for all phases of a component's life from manufacturing to damage that can destroy it.

Woodard, Stanley E.↗
NASA NTRS2015

Core Analysis Combining MT (TIPPER) and Dielectric Sensors (Sans EC) in Earth and Space

On terrestrial planets and moons of our solar system cores reveal details about a geological structure's formation, content, and history. The strategy for the search for life is focused first on finding water which serves as a universal solvent, and identifying the rocks which such solvent act upon to release the constituent salts, minerals, ferrites, and organic compounds and chemicals necessary for life. Dielectric spectroscopy measures the dielectric properties of a medium as a function of frequency. Reflection measurements in the frequency range from 300 kHz to 300 MHz were carried out using RF and microwave network analyzers interrogating SansEC Sensors placed on clean geological core samples. These were conducted to prove the concept feasibility of a new geology instrument useful in the field and laboratory. The results show that unique complex frequency spectra can be acquired for a variety of rock core samples. Using a combination of dielectric spectroscopy and computer simulation techniques the magnitude and phase information of the frequency spectra can be converted to dielectric spectra. These low-frequency dielectric properties of natural rock are unique, easily determined, and useful in characterizing geology. TIPPER is an Electro-Magnetic Passive-Source Geophysical Method for Detecting and Mapping Geothermal Reservoirs and Mineral Resources. This geophysical method uses distant lightning and solar wind activity as its energy source. The most interesting deflections are caused by the funneling of electrons into more electrically conductive areas like mineralized faults, water or geothermal reservoirs. We propose TIPPER to be used with SansEC for determining terrain/ocean chemistry, ocean depth, geomorphology of fracture structures, and other subsurface topography characteristics below the ice crust of Jovian moons. NASA envisions lander concepts for exploration of these extraterrestrial icy surfaces and the oceans beneath. One such concept would use a nuclear powered heated tip for melting through the ice sheath of Europa and inserting a down hole SansEC with TIPPER interface. NASA's Juno space probe already on the way to Jupiter as part of the Exploration New Frontiers Program and the planned Europa mission will conduct detailed reconnaissance of Jupiter's moon Europa and investigate whether the icy moon could harbor conditions suitable for life. It has already been observed that Jovian moons have auroras that may serve as naturally occurring active energy sources for a TIPPER instrument.

Mound, Michael C.↗
NASA NTRS1972

The determination of the satellite orbit of Mariner 9.

This paper presents a comprehensive analysis of the Mars orbital phase of the Mariner 9 trajectory as determined from Earth based radio data. Both the method and accuracy of the orbit determination process are reviewed. Analysis is presented to show the effects of Mars gravity model and node in the plane of the sky errors on the accuracy of orbit determination. In addition the long term evolution of the orbit from insertion to date is presented, and is decomposed into effects from the Mars gravity field, n-body perturbations, and solar radiation pressure. Since the orbit period is nearly commensurable with the Mars rotational period, the orbit experiences significant resonance perturbations. The primary perturbation is in-track with a maximum amplitude of 1000 km and a wavelength of 39 revolutions.

Born, G. H.↗
NASA NTRS1985

Atmospheric Effect on Remote Sensing of the Earth's Surface

Radiative transfer theory (RT) for an atmosphere with a nonuniform surface is the basis for understanding and correcting for the atmospheric effect on remote sensing of surface properties. In the present work the theory is generalized and tested successfully against laboratory and field measurements. There is still a need to generalize the RT approximation for off-nadir directions and to take into account anisotropic reflectance at the surface. The reflectance at the surface. The adjacency effect results in a significant modification of spectral signatures of the surface, and therefore results in modification of classifications, of separability of field classes, and of spatial resolution. For example, the 30 m resolution of the Thematic Mapper is reduced to 100 m by a hazy atmosphere. The adjacency effect depends on several optical parameters of aerosols: optical thickness, depth of aerosol layer, scattering phase function, and absorption. Remote sensing in general depends on these parameter, not just adjacency effects, but they are not known well enough for making accurate atmospheric corrections. It is important to establish methods for estimating these parameters in order to develop correction methods for atmospheric effects. Such estimations can be based on climatological data, which are not available yet, correlations between the optical parameters and meteorological data, and the same satellite measurements of radiances that are used for estimating surface properties. Knowledge about the atmospheric parameters important for remote sensing is being enlarged with current measurements of them.

Fraser, R. S.↗
NASA NTRS2012

Variable Sampling Mapping

The performance of an optical system (for example, a telescope) is limited by the misalignments and manufacturing imperfections of the optical elements in the system. The impact of these misalignments and imperfections can be quantified by the phase variations imparted on light traveling through the system. Phase retrieval is a methodology for determining these variations. Phase retrieval uses images taken with the optical system and using a light source of known shape and characteristics. Unlike interferometric methods, which require an optical reference for comparison, and unlike Shack-Hartmann wavefront sensors that require special optical hardware at the optical system's exit pupil, phase retrieval is an in situ, image-based method for determining the phase variations of light at the system s exit pupil. Phase retrieval can be used both as an optical metrology tool (during fabrication of optical surfaces and assembly of optical systems) and as a sensor used in active, closed-loop control of an optical system, to optimize performance. One class of phase-retrieval algorithms is the iterative transform algorithm (ITA). ITAs estimate the phase variations by iteratively enforcing known constraints in the exit pupil and at the detector, determined from modeled or measured data. The Variable Sampling Mapping (VSM) technique is a new method for enforcing these constraints in ITAs. VSM is an open framework for addressing a wide range of issues that have previously been considered detrimental to high-accuracy phase retrieval, including undersampled images, broadband illumination, images taken at or near best focus, chromatic aberrations, jitter or vibration of the optical system or detector, and dead or noisy detector pixels. The VSM is a model-to-data mapping procedure. In VSM, fully sampled electric fields at multiple wavelengths are modeled inside the phase-retrieval algorithm, and then these fields are mapped to intensities on the light detector, using the properties of the detector and optical system, for comparison with measured data. Ultimately, this model-to-data mapping procedure enables a more robust and accurate way of incorporating the exit-pupil and image detector constraints, which are fundamental to the general class of ITA phase retrieval algorithms.

Smith, Jeffrey, S.↗
NASA NTRS1988

Modelling of SAR polarisation phase difference from trees

The data for polarization phase difference Delta Phi between the HH- and VV-polarized backscattered waves from tree-covered fields were obtained with an airborne synthetic aperture radar at 1.225 GHz. The mean values over tree-covered fields were derived from the images of the phase difference and were examined as a function of incident beam angle from 15 to 55 deg. A theoretical model for simulating these data, based on the electromagnetic wave scatterings from the tree trunk and its branches, both of which are assumed as very long dielectric cylinders was developed. The radius and direction of a tree branch are taken as random variables and are chosen by a Monte Carlo method to encounter the incident waves in producing the scattering events. The Monte Carlo simulated results are in good agreement with the observations within experimental uncertainty.

Mo, Tsan↗
NASA NTRS2002

MAC/GMC Code Enhanced for Coupled Electromagnetothermoelastic Analysis of Smart Composites

Intelligent materials are those that exhibit coupling between their electromagnetic response and their thermomechanical response. This coupling allows smart materials to react mechanically (e.g., an induced displacement) to applied electrical or magnetic fields (for instance). These materials find many important applications in sensors, actuators, and transducers. Recently interest has arisen in the development of smart composites that are formed via the combination of two or more phases, one or more of which is a smart material. To design with and utilize smart composites, designers need theories that predict the coupled smart behavior of these materials from the electromagnetothermoelastic properties of the individual phases. The micromechanics model known as the generalized method of cells (GMC) has recently been extended to provide this important capability. This coupled electromagnetothermoelastic theory has recently been incorporated within NASA Glenn Research Center's Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC). This software package is user friendly and has many additional features that render it useful as a design and analysis tool for composite materials in general, and with its new capabilities, for smart composites as well.

Bednarcyk, Brett A.↗
NASA NTRSDate not supplied

Slosh-Induced Ullage Collapse Validation by Computational Fluid Dynamics and Application to In-space Propellant Dynamics

Ullage collapse predictions made using Computational Fluid Dynamics (CFD) were validated then made for an in-space cryogenic propellant unsettling application. Ullage collapse is the decrease in propellant tank pressure due to cooling of the ullage gas, which can be significant for cryogenic propulsion systems. Vehicles may be developed that are robust to temperature and pressure changes caused by heat leaks, e.g., propellant tanks with high maximum operation pressures, technologies yielding active thermal conditioning, and systems with ample pressurant for conditioning. These methods are robust because additional mass, cost, and complexity are used to address cryogenic fluid management (CFM). As vehicles are optimized for increased payload capacity, tracking of events such as ullage collapse and self-pressurization in tanks will become increasingly important for propellant inventory calculations. Some ullage collapse events can be studied through ground experimentation, but propellant unsettling in and around in-space coast mission phases must be studied in the absence of an acceleration field. Computational Fluid Dynamics is a powerful tool to address this need, enabling prediction of complex physics prior to flight. Validation of the chosen CFD tool and modeling methodology was done using data from a previously conducted subscale slosh-induced ullage collapse ground test performed in part by the Japan Aerospace Exploration Agency (JAXA). A small tank was partially filled with liquid nitrogen and pressurized with gaseous nitrogen at various temperatures. The tank was oscillated laterally to induce high amplitude slosh dynamics resulting in wave breakup. Successful qualitative validation of slosh wave dynamics and quantitative validation of ullage collapse promoted confidence in extending ullage collapse predictions to a flight application. Mechanisms of ullage collapse caused by main engine cutoff while in-space were identified. Both slosh dynamics leading to engine shutdown and body dynamics following shutdown were shown to contribute to propellant unsettling and ullage collapse.

J M Brodnick↗
NASA NTRS2019

Computational Fluid Dynamics Methods Used in the Development of the Space Launch System Liftoff and Transition Lineloads Databases

The objective of this paper is to document the reasoning and trade studies that supported the selection of appropriate tools for constructing aerodynamic lineload databases for the Liftoff and Transition phases of flight for launch vehicles. These decisions were made amid the maturation of an evolving workflow for generating databases on variants of the Space Launch System launch vehicle, with most being based on results from brief developmental studies performed in response to specific, unforeseen challenges that were encountered in analyzing a given configuration. This report is intended to provide a summary of the results and the decision-making processes chronologically over the design cycles of various configurations, starting with isolated free-air bodies for the Block 1 Crew, then the Block 1B Crew and Cargo configurations, and most recently the Block 1B Crew configuration in proximity to the launch tower. The results from these analyses led to the selection of the CREATE-AV Kestrel flowsolver for simulating these problems. The need to accurately capture the expected leeward-wake flow field characteristics required the use of Delayed Detached Eddy Simulation (DDES) method, for which the vorticity magnitude was employed as the solution Adaptive Mesh Refinement (AMR) function over the off-body Cartesian grid region. In addition, the Spalart-Allmaras (SA) model is used to account for the flow turbulence effects.

Ratnayake, Nalin A.↗
NASA NTRS1985

Corrected sidereal anisotropy for underground moons

Data from underground muon telescopes in New Mexico and Bolivia are analyzed in sidereal time and anti-sidereal time in the rigidity range 20 GV to a few 100's of GV. Using both vertical and north- and south- pointing telescopes in both hemispheres, a latitude range of 70 N to 50 S is covered. It is shown that there is an anti-sidereal variation of the P 1 over 2 type, having opposite phase in the Northern and Southern Hemispheres, and maximum amplitude at mid latitudes. The anti-sidereal data are used to correct the sidereal data, using the Nagashima method (Nagashima, 1984); the resulting corrected sidereal vectors for northern hemisphere telescopes have their sidereal maxima close to 3h sidereal time, in reasonable agreement with sidereal data at higher energies from small air showers. The Nagashima correction also eliminates effects due to the reversal of the Sun's polar magnetic field which show up in the uncorrected sidereal data.

Swinson, D. B.↗